1. Field of the Invention
The present invention relates to a method of transitioning incompatible polymerization catalyst systems. More particularly, the present invention relates to a method of transitioning a first catalyst system for olefin polymerization to a second catalyst system for olefin polymerization.
2. Description of the Related Art
During the production of olefin polymers in a commercial reactor it is often necessary to transition from one type of catalyst system producing polymers having certain properties and characteristics to another catalyst system capable of producing polymers of different chemical and/or physical attributes. In the past, to accomplish an effective transition between incompatible catalysts, the first catalyzed olefin polymerization process was stopped by various techniques known in the art. The reactor was then emptied, recharged and a second catalyst was introduced into a reactor. Such catalyst conversions are time consuming and costly because of the need for a reactor shut-down for an extended period of time during transition.
Another method of transition included discontinuing the polymerization of the first catalyst system to stop polymerization and introducing a second catalyst system into the polymerization reactor. However, stopping the first catalyst system feed into the reactor does not immediately stop polymerization reactions occurring within the reactor, resulting in the production of off-spec product for extended durations. The production of the off-spec product is costly and time consuming.
There is a need, therefore for a new transitioning or polymerization process that requires less reactor down-time.
Embodiments of the present invention generally include a method of polymerizing olefin monomers. In one aspect, the method includes polymerizing olefin monomers with a first catalyst system and then polymerizing olefin monomers with a second catalyst system. At least one specific embodiment of the described processes includes providing a polymerization reactor that includes a first catalyst system, contacting olefin monomers with the first catalyst system to form polyolefin in a first polymerization reaction and introducing a catalyst killer to the polymerization reactor in an amount sufficient to terminate the first polymerization reaction. The process further includes introducing a second catalyst system to the polymerization reactor in the presence of at least a portion of the catalyst killer, wherein the at least a portion of the catalyst killer is an amount sufficient to activate the second catalyst system and contacting olefin monomers with the second catalyst system to form polyolefin in a second polymerization reaction. In a specific embodiment, the catalyst killer comprises water.
At least one specific embodiment includes introducing water into the polymerization reactor at a rate sufficient to provide a first water concentration, the first water concentration being sufficient to terminate a polymerization reaction catalyzed by a first catalyst system, adjusting the first water concentration to a second water concentration, the second water concentration being an amount sufficient to activate the bimetallic catalyst system and introducing the bimetallic catalyst system to the polymerization reactor.
In at least one embodiment, the process includes contacting one or more olefin monomers with the first catalyst system to polymerize the one or more olefin monomers and form polyolefin, introducing water into the gas phase polymerization reactor to create a water concentration sufficient to terminate the first catalyst system, reducing the water concentration to a level sufficient to activate the second catalyst system, introducing an organometallic compound to the polymerization reactor in an amount sufficient to activate at least a portion of the second catalyst compound and then introducing the second catalyst system to the gas phase polymerization reactor.